1. Field of the Invention
The present invention relates to display devices and particularly to an IPS liquid crystal display with excellent viewing angle characteristics and increased luminance.
2. Description of the Related Art
A typical liquid crystal display (LCD) includes a TFT substrate, a counter substrate, and a liquid crystal layer. On the TFT substrate, pixels each having a pixel electrode, a thin film transistor (TFT), and the like are formed in the form of a matrix. The counter substrate is disposed so as to face the TFT substrate with the liquid crystal layer sandwiched therebetween. On the surface of the counter substrate that faces the TFT substrate, color filters are formed such that they are located above the pixel electrodes. Such an LCD forms an image by controlling the transmittance of the liquid crystal molecules on a pixel-by-pixel basis.
Since LCDs are flat and lightweight, the range of their application is getting wider in various fields. For instance, small-sized LCDs are widely used in mobile phones, DSCs (digital still camera), and so on. In LCDs, viewing angle characteristics are an important issue. When an LCD has poor viewing angle characteristics, the screen luminance and the colors displayed on the screen tend to change greatly depending on viewing angles. When it comes to viewing angle characteristics, IPS (in-plane switching) LCDs are currently good. In IPS LCDs, lateral electric fields are used to drive liquid crystal molecules.
There are many variations of IPS. For example, in one IPS method, a comb-shaped pixel electrode is disposed above a planar common electrode with an insulating film placed therebetween, and the electric fields produced between the pixel electrode and the common electrode are used to rotate the liquid crystal molecules. Because this method leads to a greatly increased transmittance rate, it is currently used most frequently. In such an IPS LCD, the relations between the shape of pixel electrodes and the axis of alignment are determined such that the liquid crystal molecules within a pixel rotate in the same direction, that is, in the intended direction. Despite adoption of such a configuration, it is still difficult to cause all of the liquid crystal molecules within a pixel to rotate in the same direction. Thus, it follows that the pixel has areas in which liquid crystal molecules rotate in the opposite direction.
When a pixel has an area in which liquid crystal molecules rotate in the intended direction and an area in which liquid crystal molecules rotate in the opposite direction, the rotation of liquid crystal molecules becomes unstable at the boundary between the two areas. This phenomenon is called ‘disclination.’ The area of disclination varies with the intensity of electric fields as well, and disclination works against the screen luminance and stability sought.
JP-2008-96839-A discloses a pixel structure in which the part of a common electrode that is located in the area of disclination is removed therefrom. JP-2012-137792-A discloses a pixel structure for stabilizing the orientation of liquid crystals in which the intensity of electric fields is increased in the area of disclination. JP-2011-164661-A also discloses a pixel structure for stabilizing the orientation of liquid crystals in which a pixel electrode is bent, and disclination is allowed to occur near the bent section. Further, in the pixel structure disclosed in JP-2009-47817-A, two domains are created within a pixel, and a pixel electrode includes a bridge section located at the boundary between the two domains so that the electric fields produced from the bridge section stabilize the orientation of liquid crystals.